Trim tabs are used on motor boats and motor yachts and are intended to compensate during high-speed travel of the boat or yacht, for the flow forces which act upon the hull. By angular adjustment of a trim tab swingably mounted at the stern, the tendency of water drag to impede forward motion can be reduced and the handling of the boat improved. Such tabs also improve the effectiveness of the propeller or screw at the stern of the boat.
While trim tabs are available in a variety of configurations, they as a rule are composed of metal plates which can be provided with one or more positioning mechanisms. Upper sides of the plates can be provided with reinforcing ribs or bends or flanges.
Rapidly traveling motor boats and motor yachts, for which the exhaust gas of one or more engines are normally discharged above the surface of the water, frequently travel in such manner that the exhaust gas can be released directly into the atmosphere at the stern. The result is a significant noise level associated with the release of the exhaust into the atmosphere. While a muffler may be provided for such engines, they muffler can require structural modification of the boat or yacht in an inconvenient manner. The same applies to other noise-damping devices.
Mention should also be made of the fact that other engine fluids such as engine-cooling water, may be released at the stern of the boat or yacht as well.
In the past, moreover, the location of the engine exhaust gas outlet in the craft has been found to be a complex task which has led to the need to compromise on various requirements arising in the operation of the boat or yacht. One such requirement is to optimize exhaust-gas routing to assure the best and hence least exhaust gas back pressure. Another requirement is the reduction of exhaust noise to the fullest extent possible. Still another requirement is avoidance of the return of exhaust fumes into the cockpit of the water craft.